Zinc oxide varistors of the type used with surge arrester devices are currently prepared by batch mixing and ball milling techniques wherein the zinc oxide powder is combined with certain additive metal compounds for pressing and sintering into solid discs. After sintering, the discs are then coated with a layer of conductive metal to provide electrodes to the discs. Pressing and sintering the discs into prescribed cylindrical configurations requires a good deal of preparation time and contributes to the overall varistor costs.
The electrical properties of the varistors, for example, the exponent n and resistance R must be uniform from batch to batch to ensure uniformity of electrical characteristics among the various varistors. Removing the varistors having unacceptably low exponent values causes a decrease in the material's operating efficiency since defective varistor discs quite often must be discarded. Methods for currently reclaiming rejected zinc oxide varistor discs require that the discs be completely reprocessed including costly repressing and resintering operations.
The purpose of this invention is to provide means for forming inexpensive zinc oxide varistor electrical elements from rejected varistor discs in one embodiment and for forming high purity zinc oxide varistor discs from high purity starting materials in another embodiment.